1. Field of the Invention
This invention relates to a process for the production of gluconic acid by fermentation in aqueuos fluid containing sugar. In addition, this invention also relates to the microorganisms suitable for producing gluconic acid by fermentation in aqueuos fluid containing sugar.
2. Background Information
Gluconic acid is a multifunction carbonic acid. Due to the physiological and chemical characteristics of gluconic acid, gluconic acid is used extensively as the acid itself or as a salt of the acid, in particular a sodium salt. Gluconic acid can be used both for cleaning purposes and can also be used in the pharmaceutical, food and beverage industries. In the pharmaceutical, food and beverage industries, gluconic acid is used, in particular, as a preservative. Gluconic acid can also be used in the construction, wherein gluconic acid can be used as a cement additive to increase the cements resistance to fracture and to frost and water.
Gluconic acid can be obtained by chemical synthesis, on account of its superior selectivity, however, microbial production is preferred. A series of microorganisms such as Aspergillus and Penicilliun, many bacteria such as Gluconobacter-spec., Pseudomonas, Phytomonas, Achromobacter, Kiebsiella, Zymomonas mobilis and Acetobacter methanolicus have already been indicated as being usable for such microbial production of gluconic acid. Aspergillus niger and Gluconobacter oxidans are the most applied microorganisms. It has also been known for some time that yeast-like fungus cultures, such as Aureobasidium pullulans which are characterized by polymerizations, can form small amounts of gluconic acid (V. V. Pervozvanskii Microbiology (U.S.S.R.), 8, 149 1939!).
However, the gluconic acid formation activities thereof have been known to be so small that production on an industrial scale was out of the question.
As described comprehensively in Ullmann's "Enzyklopaedie der Technischen Chemie" Ullmann's Encyclopaedia of Industrial Chemistry!, 1989, Volume A12, page 449 ff., for microbial production of gluconic acid, essentially only Aspergillus niger (predominantly), or Gluconobacter suboxidans have been applied for the industrial production of gluconic acid, though it is known that Aspergillus niger is difficult to handle as it can cause clogging and it is unsuitable for continuous production, as cell growth and gluconic acid formation would not be possible simultaneously. On the other hand, gluconobacter has been found to produce a relatively large quantity of keto-acids during production, which keto-acids can complicate processing and isolation of the gluconic acid.